Answer:a. Retention of five functional digits on the tore and hindimbs
Step-by-step explanation:
The presence of five digits or pentadactyly on the fingers as well as on the toes makes the primates distinct from other mammals. Also the keratin nails are present on each digit makes these organisms distinct from other mammals.
The five digits on the hindlimbs helps in grip of objects and on toes helps in climbing.